Wells may be bored for various purposes, such as for accessing underground deposits. Reserves of hydrocarbons are commonly extracted through bored well-holes. The boring of well-holes and the subsequent extraction of hydrocarbons through the boreholes requires various operations to be performed underground.
Equipment may be transported in boreholes by a number of means, such as by wireline; by motorised vehicle or tractor; by pushing or injecting tubing into the borehole; or by rotation. Different underground operations require different means for transporting equipment underground. For example, operations involving pumping fluids into or out of a borehole typically require use of tubular members, such as coiled tubing.
Coiled tubing is also useful in circumstances where access using wireline tools is impeded. Where there is a blockage in a borehole or gravity is insufficient to overcome friction, coiled tubing may be preferred to wireline. However, coiled tubing operations require large equipment in comparison with wireline operations. The coiled tubing itself is heavy and the reel carrying the coiled tubing typically requires a large work area or footprint. The manipulation of coiled tubing often requires heavy lifting equipment, such as an injector that is used to insert and extract coiled tubing in the borehole.
Boreholes located underwater can be accessed from the water surface by risers. Typically a wellhead is located on the seabed and the riser provides an access conduit between the wellhead and the surface.